FIG. 1A is a cross-sectional view of prior art torque converter 10. It should be appreciated that only the top half of the torque converter is shown in FIG. 1A, since the bottom half is substantially a mirror image of the top half. Likewise, only an upper portion of thrust washer 20 is shown. Torque converter 10 is a typical torque converter including pump 12, turbine 14, and stator 16. Torque converter 10 includes prior art thrust washer 20 engaged between turbine hub 30 and piston 40. The thrust washer is essentially a thin, flat disk with the center removed. Thrust washers are necessary in many torque converters to prevent wear at the point of contact between two components which move relative to each other. Thrust washers are similar to bearings, except thrust washers use fluid lubrication instead of balls or rollers to allow for a smooth rotational motion of two components in contact.
Specifically, during operation of torque converter 10, thrust is generated on turbine hub 30, causing the hub to contact piston 40. To prevent excessive wear between hub 30 and piston 40, a thrust washer, for example, thrust washer 20, is disposed between the hub and the piston.
The following refers to FIGS. 1B, and 1C which show a front and perspective view, respectively, of prior art thrust washer 20. In order to properly operate, fluid circuits must be provided in the torque converter for cooling fluids, such as oil. An adequate flow of fluid is necessary to change and maintain fluid pressures in the torque converter, particularly for adequate clutch capacity and clutch controllability. Furthermore, thrust bearings must be able to provide a sufficient layer of lubrication to reduce the wear and friction between moving parts. Since the thrust washer blocks some of the necessary fluid circuits, provision must be made to allow fluid to pass between the inner and outer circumferences 22 and 24, respectively, of washer 20. Traditionally, to accomplish this fluid communication between the inner and outer circumferences, it is known to provide grooves 26 in face 28 of washer 20. For purposes of the description herein, the terms inner and outer circumferences may refer the entire surface defined by the inner or outer circumferences, in addition to just the edges.
Thrust washers are commonly made out of polymers, or plastics, since it is easy to mold grooves into a plastic thrust washer. Unfortunately, plastic thrust washers are quite expensive to produce. Therefore, steel thrust washers are sometimes used, since steel washers are cheaper than their plastic counterparts. However, grooves can not be simply stamped into the steel washers, because this would create protrusions on the face of the washer opposite face from each groove. Such protrusions are not acceptable, because they would detract from the performance of the washers. Therefore, each groove must be machined into the face of steel thrust washers, greatly increasing the cost and time required to make each thrust washer.
Thus, there is a long-felt need for thrust washers which provide the same fluid flow communication as prior art washers, but which can be more cheaply manufactured.